Hello Cirrus People
I am hoping to tap into your experience to help solve an issue with a customers SR20.
I have recently been brought on board to a problem that we (the company I work for), have been trying to resolve since 2019. The Customer isn’t confident flying the plane. Now that I have been brought onto the problem, I have flown with the customer, and seen/felt the engine momentary loss of power. Let’s call this momentary loss of power, an event.
The event as I call it, presents as a momentary 1 - 2 second, feeling of a loss of engine power. You will feel the aircraft slow momentarily, and you come forward in your seat slightly. The tachomer shows a reduction in RPM from cruise RPM, then an increase from cruise RPM as the power returns, then the RPM settles back to cruise RPM. There is no noticeable movement in Manifold Pressure or Fuel Flow indications. But lets just say it gets your attention.
Note: The owner notes that the first time this happened, it lasted approximately 20 senconds.
1999 Cirrus SR20 SN 1021
History and Troubleshooting
When the first event happened, it was attributed to something wrong with the engine fuel system. The fuel manifold valve, metering valve, fuel pump were removed, Overhauled and reinstalled. The fuel system was then adjusted for pressures (aka - portatest).
The event re-occurred.
Fuel Nozzles were cleaned. Ref SID05-7
The event re-occurred
The propeller governor was removed for bench test. (Now here is where I get involved). The propeller was reinstalled. Static RPM was noted low at 2625, with the governor Max RPM screw backed out as far as it would go. The Hartzell propeller fined pitch adjustment was completed to give a max static RPM of approx 2700. Then the governor Max RPM screw was turned in to give a max static RPM of approx 2650 (per the Cirrus MM).
The event re-occurred. This time I was along with the owner, and I felt/saw the event.
When I first experienced the event, my initial gut instinct was the the engine momentarily ingested a small amount of water. I added 300 ml of isopropyl alcohol to each fuel tank to absorb any water into solution into the fuel. Also, the owner is very consistent with checking his fuel sumps prior to flight. The event has also been known to occur when the fuel is selected from both L and R tanks.
Flew with the owner again. The event re-occurred. During this flight, I also monitored the Manifold Pressure and Fuel Flow gauges for fluctuations. No fluctuations noted. We also did an in flight magneto check, which resulted in nothing abnormal. However, it was noted that the loss of power due to shutting one magneto down, was significantly less than the loss of power during these momentary events.
My thought was that it may be ignition related. We disconnected the P lead from the LH magneto.
Note: This aircraft has been modified/equipped with a Surefly Electronic Ignition system on the RH side.
Flew with the owner again. The event re-occurred.
The event seems to occur after a half hour flight, and at cruise power setting. Although, the owner notes that it happened once, not too long after take-off, and may have been at a climb power setting.
Total time since first event = 58 hrs
The Surefly Electronic Ignition system was installed after the events began to occur. Therefore, the Electronic Ignition system should not be the cause.
The Surefly system is also known to add approx 10° F to CHT.
Spark plugs are cleaned, gapped and tested every annual inspection.
Firewall fuel filter inspected and cleaned every annual inspection.
On take-off, CHTs can exceed 420°F. And cruise temps seem to be in the 380°F range. Also, when nosing/powering the aircraft up for a cruise climb, temps can also exceed 400°F again. This seems high to me. (However, admittedly, I am more of a Cessna new and old school 182 guy.) But I seem to hear that high temps are more common on the Cirrus???
What does an engine need to run… Air, Fuel and Ignition.
I can’t see there being a significant enough blockage to cause choking of induction air. Especially of a recurring nature.
We’ve been through the engine fuel system enough to say it shouldn’t be part of the engine fuel system, and the fact that it occurs on both L and R fuel tanks should indicate that airframe fuel starvation should not be the cause.
In flight magneto checks and removal of the P lead don’t provide any change. Shouldn’t be anything ignition related.
What Am I missing???
What are the chances that this is a momentary vapor lock in the fuel system?
I’m hoping that someone else in the Cirrus world has experienced this. Point us in the right direction before we beat our heads on the wall. We are open to suggestions.
Cheers, and thanks in advance for the help.